From 114692655060bf74d01e0f5452e89f3bd332dfa1 Mon Sep 17 00:00:00 2001 From: Kyotaro Horiguchi Date: Thu, 24 Jan 2019 13:35:19 +0900 Subject: [PATCH] Add control on wheter symbols in external module is exported We load exteral modlues with RTLD_GLOBAL, which is problematic when two or more modules share the same symbol. On the other hand some modules mandates to export its symbols. This patch enables modules to decide whether to export them or not. They is defaultly hidden. plpython module is modified along with as it needs to export symbols. --- doc/src/sgml/xfunc.sgml | 8 ++++++++ src/backend/utils/fmgr/dfmgr.c | 13 ++++++++++++- src/include/fmgr.h | 8 ++++++++ src/pl/plpython/plpy_main.c | 1 + 4 files changed, 29 insertions(+), 1 deletion(-) diff --git a/doc/src/sgml/xfunc.sgml b/doc/src/sgml/xfunc.sgml index e18272c33a..9a65e76eda 100644 --- a/doc/src/sgml/xfunc.sgml +++ b/doc/src/sgml/xfunc.sgml @@ -1875,6 +1875,14 @@ PG_MODULE_MAGIC; (Presently, unloads are disabled and will never occur, but this may change in the future.) + + The dynamic loader loads a file as its symbols are hidden from external + modules by default. A file is loaded exporting the symbols by writhing + this in one of the module source files. + +PG_MODULE_EXPORT_SYMBOL; + + diff --git a/src/backend/utils/fmgr/dfmgr.c b/src/backend/utils/fmgr/dfmgr.c index 456297a531..98ac1cc438 100644 --- a/src/backend/utils/fmgr/dfmgr.c +++ b/src/backend/utils/fmgr/dfmgr.c @@ -236,7 +236,7 @@ internal_load_library(const char *libname) #endif file_scanner->next = NULL; - file_scanner->handle = dlopen(file_scanner->filename, RTLD_NOW | RTLD_GLOBAL); + file_scanner->handle = dlopen(file_scanner->filename, RTLD_NOW | RTLD_LOCAL); if (file_scanner->handle == NULL) { load_error = dlerror(); @@ -281,6 +281,17 @@ internal_load_library(const char *libname) errhint("Extension libraries are required to use the PG_MODULE_MAGIC macro."))); } + /* Check if the module wants to export symbols */ + if (dlsym(file_scanner->handle, PG_MODULE_EXPORT_SYMBOL_NAME_STRING)) + { + elog(DEBUG3, + "loaded dynamic-link library \"%s\" with RTLD_GLOBAL", libname); + /* want to export, reload it the way */ + dlclose(file_scanner->handle); + file_scanner->handle = dlopen(file_scanner->filename, + RTLD_NOW | RTLD_GLOBAL); + } + /* * If the library has a _PG_init() function, call it. */ diff --git a/src/include/fmgr.h b/src/include/fmgr.h index ead17f0e44..c072850646 100644 --- a/src/include/fmgr.h +++ b/src/include/fmgr.h @@ -456,6 +456,14 @@ PG_MAGIC_FUNCTION_NAME(void) \ } \ extern int no_such_variable +#define PG_MODULE_EXPORT_SYMBOL_NAME Pg_module_exrpot_symbols +#define PG_MODULE_EXPORT_SYMBOL_NAME_STRING "Pg_module_exrpot_symbols" + +#define PG_MODULE_EXPORT_SYMBOL \ +extern PGDLLEXPORT void PG_MODULE_EXPORT_SYMBOL_NAME(void); \ +extern PGDLLEXPORT void PG_MODULE_EXPORT_SYMBOL_NAME(void){} + + /*------------------------------------------------------------------------- * Support routines and macros for callers of fmgr-compatible functions diff --git a/src/pl/plpython/plpy_main.c b/src/pl/plpython/plpy_main.c index 6a66eba176..9165b5f455 100644 --- a/src/pl/plpython/plpy_main.c +++ b/src/pl/plpython/plpy_main.c @@ -42,6 +42,7 @@ extern void _PG_init(void); PG_MODULE_MAGIC; +PG_MODULE_EXPORT_SYMBOL; PG_FUNCTION_INFO_V1(plpython_validator); PG_FUNCTION_INFO_V1(plpython_call_handler); -- 2.16.3